1. Field of the Invention
The invention relates to semiconductor electromagnetic radiation sources which may be modulated, and in particular to semiconductor infrared sources capable of modulation. According to this invention, a semiconductor body is provided with means for causing it thermally to emit broadband infrared radiation in a spectrum of interest at a meaningful intensity, and also with modulating means for controllably modifying the emission of such radiation, thereby modulating the output intensity of the device. The modulating means controls the presence of carriers within the body, correspondingly to modify the emission of such radiation from the body. The presence of carriers may be controlled optically and it may be controlled electrically.
2. Prior Art
LED devices are known in the prior art and operate by injecting carriers into the semiconductor so that when electrons and holes recombine, radiation within a narrow optical spectrum is emitted, provided the band structure favors this emission (direct band gap materials). Thus, this class of device depends upon the presence of free carriers which, upon electron-hole recombination, causes the device to emit. When used as infrared sources, such devices require cooling for effective operation and, as noted, the injection of free carriers causes the emission.
Another class of device is also known for providing a source of infrared radiation and this type of device uses heated filaments, heated cavities or various arc techniques. These devices are externally modulated, usually with a mechanical chopper wheel. Mechanical chopper wheel devices have been developed so as periodically to block or mask the light emitted by such sources. Such choppers are cumbersome and are limited mechanically so that restriction of speed at which the modulation may be effected is inherent.
The switching of semiconductor devices by means of optical input is known from the Myers U.S. Pat. No. 4,240,088 of Dec. 16, 1980, whereas switching by means of thermal input is known from the Nakata U.S. Pat. No. 4,009,482 of Feb. 27, 1977, the Murphy et al U.S. Pat. No. 3,962,692 of June 8, 1976 and the Jaskoluski et al U.S. Pat. No. 4,050,083 Sept. 20, 1977.
It is also known to utilize semiconductor bodies integrally formed with light-emissive semiconductor devices from the Vasudev U.S. Pat. No. 4,388,633 June 14, 1983, the Chapman et al U.S. Pat. No. 4,231,149 Nov. 4, 1980 and the Carballes U.S. Pat. No. 4,202,000 of May 6, 1980.
Other U.S. patents of interest are the Esaki et al U.S. Pat. No. 4,163,238, the Nakata U.S. Pat. No. 4,127,792, the Byatt et al U.S. Pat. No. 4,090,212 and the Dahlberg U.S. Pat. No. 3,504,240.